The field of the present invention pertains to apparatus and methods for detecting sparks, flames or fire. More particularly, the invention relates to a process and system for detecting a spark, flame or fire with increased sensitivity, faster processing and response times, and greater intelligence for discriminating against false alarms.
To prevent fires, and the resulting loss of life and property, the use of flame detectors or flame detection systems is not only voluntarily adopted in many situations, but is also required by the appropriate authority for implementing the National Fire Protection Association""s (NFPA) codes, standards, and regulations. Facilities faced with a constant threat of fire, such as petrochemical facilities and refineries, semiconductor fabrication plants, paint facilities, co-generation plants, aircraft hangers, silane gas storage facilities, gas turbines and power plants, gas compressor stations, munitions plants, airbag manufacturing plants, and so on are examples of environments that typically require constant monitoring and response to fires and potential fire hazard situations.
To convey the significance of the fire detection system and process proposed by this patent application, an exemplary environment, in which electrostatic coating or spraying operations are performed, is explained in some detail. However, it should be understood that the present invention may be practiced in any environment faced with a threat of fire.
Electrostatic coating or spraying is a popular technique for large-scale application of paint, as for example, in a production painting line for automobiles and large appliances. Electrostatic coating or spraying involves the movement of very small droplets of electrically charged xe2x80x9cliquidxe2x80x9d paint or particles of electrically charged xe2x80x9cPowderxe2x80x9d paint from an electrically charged (40 to 120,000 volts) nozzle to the surface of a part to be coated.
While facilitating efficiency, environmental benefits, and many production advantages, electrostatic coating of parts in a production paint line, presents an environment fraught with fire hazards and safety concerns. For example, sparks are common from improperly grounded workpieces or faulty spray guns. In instances where the coating material is a paint having a volatile solvent, the danger of a fire from sparking, or arcing, is, in fact, quite serious. Fires are also a possibility if electrical arcs occur between charged objects and a grounded conductor in the vicinity of flammable vapors.
Flame detectors have routinely been located at strategic positions in spray booths to monitor any fires that may occur and to shut down the electrostatics, paint flow to the gun, and conveyors in order to cut off the contributing factors leading to the fire.
Three primary contributing factors to a fire are: (1) fuel, such as atomized paint spray, solvents, and paint residues; (2) heat, such as that derived from electrostatic corona discharges, sparking, and arcing from ungrounded workpieces, and so on; and (3) oxygen. If the fuel is heated above its ignition temperature (or xe2x80x9cflash pointxe2x80x9d) in the presence of oxygen, then a fire will occur.
An electrical spark can cause the temperature of a fuel to exceed its ignition temperature. For example, in a matter of seconds, a liquid spray gun fire can result from an ungrounded workpiece producing sparks, as the spray gun normally operates at very high voltages (in the 40,000 to 120,000 volt range) . An electrical spark can cause the paint (fuel) to exceed its ignition temperature. The resulting spray gun fire can quickly produce radiant thermal energy sufficient to raise the temperature of the nearby paint residue on the booth walls or floor, causing the fire to quickly spread throughout the paint booth.
A fire may self-extinguish if one of the three above- mentioned contributing factors is eliminated. Thus, if the fuel supply of the fire is cut off, the fire typically stops. If a fire fails to self-extinguish, flame detectors are typically expected to activate suppression agents to extinguish the fire and thereby prevent major damage.
Flame detectors, which are an integral part of industrial operations such as the one described above, must meet standards set by the NFPA, which standards are becoming increasingly stringent. Thus, increased sensitivity, faster reaction times, and fewer false alarms are not only desirable, but are now a requirement.
There is a need for a sensitive, reliable and effective method and system for detecting sparks, flames, or fire with little or no interruptions caused by false alarms.
The present invention is directed in various aspects to a sensitive, reliable, intelligent and effective method and system for detecting sparks, flames or fire while reducing or eliminating interruptions caused by false alarms.
In a first aspect, a microprocessor-controlled detector advantageously senses temporal radiant energy in two different optical frequency ranges, such as, e.g., the MIR and VIS frequency ranges. Sensing temporal radiant energy in two different optical frequency ranges can be advantageously used to measure temporal radiant energy emitted from the environment, on the one hand, and temporal radiant energy emitted from false alarm sources on the other hand. Using mathematical techniques, such as, e.g., Fourier Transform analysis, the detector generates a first spectrum of frequency components from the temporal radiant energy sensed in the first optical frequency range, and a second spectrum of frequency components from the temporal radiant energy sensed in the second optical frequency range. In a preferred embodiment, the first and second spectra are respectively power spectra. The first and second spectra preferably represent a moving average. For example, a moving average of a spectrum can be generated by generating the spectrum every one-quarter second and averaging the four most current spectra over a one second time segment.
The detector then preferably performs a frequency bin subtraction on the two spectra of frequency components, i.e., a compensated spectrum of frequency components is generated by subtracting the second spectrum of frequency components from the first spectrum of frequency components. Preferably, the second spectrum of frequency components is scaled using a scaling factor equal to the ratio between the average amplitude of the first spectrum of frequency components over the second spectrum of frequency components. The compensated spectrum of frequency components is then analyzed to determine whether an unknown phenomenon represents an unwanted fire, or at least a possibility of an unwanted fire. In the preferred embodiment, an average amplitude and centroid of the compensated spectrum of frequency components are obtained. The greater the average amplitude and the more the centroid is centered between 2 Hz and 10 Hz, the greater the change that an unwanted fire exists.
In another aspect, a plurality of reference compensated spectra of frequency components are obtained from each of a variety of known unwanted fire sources and known false alarm sources. The respective average amplitudes and centroids of the reference compensated spectra are constructed into feature space coordinates, i.e., amplitude-centroid coordinates, and plotted on a feature space scatter plot. A fire detection boundary, which excludes substantially all of the feature space coordinates originating from known false alarm sources, is defined on the scatter plot. The fire detection boundary is then stored in memory for later comparison to when an unknown phenomenon is detected.
When the unknown phenomenon is detected, a compensated spectrum of frequency components is generated. The average amplitude and centroid of the compensated spectrum is then preferably constructed into a feature space coordinate, the location of which with respect to the fire detection boundary is indicative of whether the unknown phenomenon presents an unwanted fire situation. In particular, inclusion of the feature space coordinate inside the fire detection boundary indicates that the unknown phenomenon presents an unwanted fire situation. On the contrary, exclusion of the feature space outside the fire detection boundary indicates that the unknown phenomenon presents an unwanted fire detection. During detection of the unknown phenomenon, the fire detection boundary can be adjusted based on radiant energy sensed in a third optical frequency band, such as, e.g., the NIR frequency range.
Further embodiments, variations, modifications and enhancements are also disclosed herein.